Many medical procedures in use today require a relatively small sample of blood, in the range of 5-50 .mu.L. It is more cost effective and less traumatic to the patient to obtain such a sample by lancing or piercing the skin at a selected location, such as the finger, to enable the collection of 1 or 2 drops of blood, than by using a phlebotomist to draw a tube of venous blood. With the advent of home use tests such as self monitoring of blood glucose, there is a requirement for a simple procedure which can be performed in any setting by a person needing to test.
The centuries-old practice of cupping has survived into modern times. Cupping is a treatment in which evacuated glass cups are applied to intact skin in order to draw blood toward or through the surface. The cuppist pierces the skin and uses suction cups to draw out blood. That method was used as a therapeutic procedure for disorders associated with an excess of blood (high blood pressure, circulation problems and muscular pain), one of the four humors of medieval physiology.
A more recent application for cupping has been the withdrawal of blood from a wound for the purpose of applying the blood to a diagnostic test strip. An instrument employed for that purpose comprises an inverted cup-shaped element having a piston. After an incision has been made in the skin by a separate lancet, the piston is depressed, against the bias of a spring, and a rim of the cup-shaped element is applied against the skin in surround relationship to the incision. By then releasing the piston for extension by the spring a vacuum is created around the incision to draw a drop of blood therefrom. Such an instrument is made by Nipuro Medical Equipment K.K. in Tokyo, Japan.
A shortcoming of such an instrument is the inconvenient need for the user to manipulate two separate pieces of equipment, i.e. the lancet and the suction device.
Lancets in conventional use generally have a rigid body and a sterile needle which protrudes from one end. The lancet may be used to pierce the skin, thereby enabling the collection of a blood sample from the opening created. The blood is transferred to a test device or collection device. Blood is most commonly taken from the fingertips, where the supply is generally excellent. However, the nerve density in this region causes significant pain in many patients. Sampling of alternate site, such as earlobes and limbs, is sometimes practiced to access sites which are less sensitive. These sites are also less likely to provide excellent blood samples and make blood transfer directly to test devices difficult.
Repeated lancing in limited surface areas (such as fingertips) results in callous formation. This leads to increased difficulty in drawing blood and increased pain.
To reduce the anxiety of piercing the skin and the associated pain, many spring loaded devices have been developed. The following two patents are representative of the devices which were developed in the 1980's for use with home diagnostic test products.
Cornell et al. U.S. Pat. No. 4,503,856 describes a spring loaded lancet injector. The reusable device interfaces with a disposable lancet. The lancet holder may be latched in a retracted position. When the user contacts a release, a spring causes the lancet to pierce the skin at high speed and then retract. The speed is important to reduce the pain associated with the puncture.
Levin et al. U.S. Pat. No. 4,517,978 describes a blood sampling instrument. This device, which is also spring loaded, uses a standard disposable lancet. The design enables easy and accurate positioning against a fingertip so the impact site can be readily determined. After the lancet pierces the skin, a bounce back spring retracts the lancet to a safe position within the device.
In institutional settings, it is often desirable to collect the sample from the patient and then introduce the sample to a test device in a controlled fashion. Some blood glucose monitoring systems, for example, require that the blood sample be applied to a test device which is in contact with a test instrument. In such situations, bringing the finger of a patient directly to the test device poses some risk of contamination from blood of a previous patient. With such systems, particularly in hospital settings, it is common to lance a patient, collect a sample in a micropipette via capillary action and then deliver the sample from the pipette to the test device.
Haynes U.S. Pat. No. 4,920,977 describes a blood collection assembly with lancet and microcollection tube. This device incorporates a lancet and collection container in a single device. The lancing and collection are two separate activities, but the device is a convenient single disposable unit for situations when sample collection prior to use is desirable. Similar devices are disclosed in Sarrine U.S. Pat. No. 4,360,016, and O'Brien U.S. Pat. No. 4,924,879.
Jordan et al. U.S. Pat. Nos. 4,850,973 and 4,858,607, disclose a combination device which may be alternatively used as a syringe-type injection device and a lancing device with disposable solid needle lancet, depending on configuration.
Lange et al. U.S. Pat. No. 5,318,584 describes a blood lancet device for withdrawing blood for diagnostic purposes. This invention uses a rotary/sliding transmission system to reduce the pain of lancing. The puncture depth is easily and precisely adjustable by the user.
It has also been proposed to provide a skin-lancing device with a vacuum-generating device in a single housing, to enable a blood sample to be forcefully suctioned out of an incision made by the skin-lancing device.
Exemplary of such devices are: Garcia et al. U.S. Pat. No. 4,637,403; Haber et al. U.S. Pat. No. 5,21 7,480; Suzuki et al. U.S. Pat. No. 5,368,047; Dombrowski U.S. Pat. No. 4,653,513; and Bodicky et al. U.S. Pat. No. 5,320,607. In the Bodicky et al. patent the lancet is fixed to a suction plunger which can be retracted, along with the lancet, to create a vacuum after the skin has been pierced by the lancet. The need to retract the lancet along with the plunger to create a vacuum complicates the design of the internal structure of the apparatus.
The Suzuki et al. patent discloses a suction plunger which serves not only as a vacuum generator, but also as an actuator for releasing a cocked lancet for firing.
Erickson et al. U.S. Pat. No. 5,582,184, describes a means of collecting and measuring body fluids. This system uses a coaxial hollow lancet and capillary tube disposed within a spacer member. The spacer member limits the depth of lancet penetration, and compresses body tissue around the lancet while the lancet is in the skin, for improving the flow of interstitial fluid to the incision. However, the incision may tend to close around the lancet, thereby limiting the amount of body fluid that can be obtained.
Single use devices have also been developed for single use tests, i.e. home cholesterol testing, and for institutional use to eliminate cross-patient contamination multi-patient use. Crossman et al. U.S. Pat. No. 4,869,249, and Swierczek U.S. Pat. No. 5,402,798, also disclose disposable, single use lancing devices.
U.S. Pat. Nos. 5,421,816; 5,445,611 and 5,458,140 disclose, as a replacement for invasive sampling, the use of ultrasound to act as a pump for expressing interstitial fluid directly through intact (i.e., non-lanced) skin. The amount of fluid which can be obtained by way of such non-invasive vibration is minimal, however.
The disclosures of the above patents are incorporated herein by reference.
Even with the many improvements which have been made, the pain associated with lancing remains a significant issue for many patients. The need for blood sampling and the fear of the associated pain is also a major obstacle for the millions of diagnosed diabetics, who do not adequately monitor their blood glucose due to the pain involved. Moreover, lancing to obtain a blood sample for other diagnostic applications is becoming more commonplace, and a less painful, minimally invasive device is needed to enhance those applications and make those technologies more acceptable.
An object of the present invention therefore, is to provide a device and a method for obtaining a sample of bodily fluid through the skin which is virtually pain free and minimally invasive, particularly by penetrating less sensitive areas of the skin.
Furthermore, known lancing devices include manually actuable buttons for triggering the lance-driving mechanism once the user has placed the device against his/her skin. Because the user knows the precise instant when the lancet will be triggered and pain will be felt, there is a tendency for the user to jerk or raise the device at the instant of triggering, which can lead to inconsistent skin penetration, or possibly no penetration. Therefore, a further object of the invention is to provide a lancing device which eliminates such a tendency on the part of the user.
Therefore, it is another object of the invention to provide a lancet carrier which eliminates the above-mentioned shortcomings.
Another object of this invention is to provide a method which can result in a sample of either blood or interstitial fluid, depending on the sample site and the penetration depth utilized. While there are no commercially available devices utilizing interstitial fluid (ISF) at this time, there are active efforts to establish the correlation of analytes, such as glucose, in ISF compared to whole blood. If ISF could be readily obtained and correlation is established, ISF may be preferable as a sample since there is no interference of red blood cells or hematocrit adjustment required.
Another object of this invention is to provide a method which can draw a small but adjustable sample, i.e. 3 .mu.L for one test device and 8 .mu.L for another test device, as appropriate.
It is a further object of the invention to provide a device for minimally invasive sampling comprising a reusable sampler and disposable sample lancet and collection device.